Like all flies, the Chironomidae are holometabolous, and undergo metamorphosis in their life cycle. Adult females lay eggs in aquatic habitats. The larvae that hatch from these are often planktonic in their first instar, floating in the water column and feeding on microscopic particles in the water. After their first molt, larvae of most species descend to the bottom and remain benthic through the rest of the larval stage (usually four instars). The larvae transforms into a pupa, which often stays within a shelter or cocoon while it transforms into an adult. When it's time to emerge, the pupa swims to the surface, and the adult pulls itself out of its old skin.
Development - Life Cycle: metamorphosis
The Chironomidae is a large and diverse family of flies. They are commonly known as "non-biting midges." There are over 20,000 species known world-wide, including 2,000 in the Nearctic. Adult midges are relatively small (1-20 mm long), with narrow bodies and long legs. They are often confused with mosquitos, but no members of this family are blood-feeders (hence the "non-biting" part of the common name). Adults, if they feed at all, feed on nectar or similar substances. Midge larvae are nearly all aquatic or sub-aquatic, and are a very important part of many freshwater ecosystems. Both in numbers and in diversity, they are often the largest group of primary consumers in these systems. Species of Chironomidae can be found in an enormous variety of aquatic habitats, from brackish estuaries to pools in tree-holes, and from low-oxygen lake sediments to fast-flowing mountain streams.
Chironomids are the most diverse and abundant macroinvertebrates in most of the aquatic ecosystems they inhabit (and they inhabit most aquatic ecosystems). Most natural ponds, lakes and streams are home to 50-100 different species of non-biting midges. Collectively, they play a vital role in freshwater ecosystems as primary consumers. They harvest an enormous amount of energy from detritus and are one of the major supports for animal communities in these systems.
The many thousands of chironomid species have many different feeding habits. Most species feed on small particles of organic debris, but the size of particles varies, some shred bits of dead wood and leaves, some gather smaller particles, some even filter tiny particles suspended in the water. Some of these detritivores also collect algae cells, and some species are herbivores, specialize in feeding on algae. Other herbivores are "miners" tunneling in larger vascular plants. There are some fungivore chironomids as well, eating spores and grazing on hyphae. A few species are simple predators, often attacking other chironomid species.
Primary Diet: detritivore
Species of chironomid midges are found in moist or wet habitats in all major landmasses of the world, including Antarctica, and most islands.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); antarctica (Native ); oceanic islands (Native )
Other Geographic Terms: cosmopolitan
Midge larvae occur in all kinds of benthic freshwater habitats, including the bottoms of streams, rivers, lakes, ponds, and temporary pools, also wetlands such as marshes and swamps. Some breed in isolated damp habitats such as tree-holes, pitcher plants, patches of moist soil, even dung pats. The "blood midges" or "bloodworms" are species of midges with hemoglobin in their hemolymph, which allows them to survive in low-oxygen (and often heavily-polluted) habitats. Adults rarely disperse far from the larval habitat.
Habitat Regions: temperate ; tropical ; polar ; terrestrial ; freshwater
Terrestrial Biomes: forest ; rainforest
Aquatic Biomes: benthic ; lakes and ponds; rivers and streams; temporary pools; brackish water
Wetlands: marsh ; swamp ; bog
Other Habitat Features: riparian ; estuarine ; intertidal or littoral
Lifespan varies greatly between and within species in the Chironomidae. Individual growth and development rates are strongly influenced by temperature and other environmental factors. Many temperate species live for a year, surviving the winter as larvae. Some species are known to complete entire life-cycles in a few weeks, if temperatures are warm and food is abundant.
Adults are small (1-20 mm long, most less than 10 mm), slim, long-legged flies. They resemble, and are often confused with, mosquitoes (Culicidae), but unlike mosquitoes, they do not bite, and have no scales on their wings. Many species rest on their hind two pairs of legs, and hold their forelegs out in front of them. In most species, adult males have plumose antennae that are much larger than the females (these are probably used to locate females). Most species are dark-colored, usually brown or black.
Larvae are elongate and cylindrical, with distinct segmentation and a hard sclerotized head capsule that cannot be retracted into the body. They have no true legs, but do have a pair of unjointed "prolegs" on the first segment of the thorax. The presences of this pair of prolegs, the absence of true legs, and the structure of the head are good distinguishing marks for identifying larvae in the Chironomidae. Color varies widely among larvae, most are tan or brown, but some are whitish, some are green. Larvae of a number of species in the subfamily Chironominae have the hemoglobin in their circulatory fluid, which helps them survive in low-oxygen habitats. These larvae are pinkish or red when alive, and are often called "blood midges."
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
Sexual Dimorphism: sexes shaped differently
Non-biting midges are so abundant in so many freshwater habitats that practically every kind of predator in these habitats feeds on them at some stage of their life cycle. Midges try to avoid predation by limiting their activity during daylight, and larvae and pupae take refuge in tunnels that they build in sediment. Many species are cryptically colored.
Anti-predator Adaptations: cryptic
Adult non-biting midges often form mating swarms, either in the air near oviposition sites, or "skating" on the surface of water. These swarms are composed mostly of males, and may serve to attract females.
In most species, eggs are laid in gelatinous masses on the water surface or on emergent vegetation. In some species, females lay their eggs in or under the water. Adult chironomids usually only live for a few days or weeks, and so reproduction is a single concerted effort. Most species breed seasonally. A very few species are reported to be parthenogenic, most have male and female adults
Key Reproductive Features: semelparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); parthenogenic ; sexual ; fertilization (Internal ); oviparous
No male investment. Female investment is in provisioning eggs and producing a protective gel mass for them.
Parental Investment: pre-fertilization (Provisioning)
The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many species superficially resemble mosquitoes, but they lack the wing scales and elongated mouthparts of the Culicidae.
The name Chironomidae stems from the Ancient Greek word kheironómos, "a pantomimist".
This is a large taxon of insects; some estimates of the species numbers suggest well over 10,000 world-wide.[2] Males are easily recognized by their plumose antennae. Adults are known by a variety of vague and inconsistent common names, largely by confusion with other insects. For example, chironomids are known as "lake flies" in parts of Canada and Lake Winnebago, Wisconsin, but "bay flies" in the areas near the bay of Green Bay, Wisconsin. They are called "sand flies", "muckleheads",[3] "muffleheads",[4] "Canadian soldiers",[5] or "American soldiers"[6] in various regions of the Great Lakes area. They have been called "blind mosquitoes" or "chizzywinks" in Florida.[7] In Kansas, they are known as "midges."[8] However, they are not mosquitoes of any sort, and the term "sandflies" generally refers to various species of biting flies unrelated to the Chironomidae.
The group includes the wingless Belgica antarctica, the largest terrestrial animal of Antarctica.[9][10]
Their larvae produce silk, and Chironomus has been studied as an alternative source of silk other than the silk moth, as it is possible to extract it without killing the animal (Ahimsa silk).[11]
The biodiversity of the Chironomidae often goes unnoticed because they are notoriously difficult to identify and ecologists usually record them by species groups. Each morphologically distinct group comprises a number of morphologically identical (sibling) species that can only be identified by rearing adult males or by cytogenetic analysis of the polytene chromosomes. Polytene chromosomes were originally observed in the larval salivary glands of Chironomus midges by Balbiani in 1881. They form through repeated rounds of DNA replication without cell division, resulting in characteristic light and dark banding patterns which can be used to identify inversions and deletions which allow species identification.
Larval stages of the Chironomidae can be found in almost any aquatic or semiaquatic habitat, including treeholes, bromeliads, rotting vegetation, soil, and in sewage and artificial containers. They form an important fraction of the macro zoobenthos of most freshwater ecosystems. They are often associated with degraded or low-biodiversity ecosystems because some species have adapted to virtually anoxic conditions and are dominant in polluted waters. Larvae of some species are bright red in color due to a hemoglobin analog; these are often known as "bloodworms".[12] Their ability to capture oxygen is further increased by their making undulating movements.[13]
Many reference sources in the past century or so have repeated the assertion that the Chironomidae do not feed as adults, but an increasing body of evidence contradicts this view. Adults of many species do, in fact, feed. The natural foods reported include fresh fly droppings, nectar, pollen, honeydew, and various sugar-rich materials.[2]
The question whether feeding is of practical importance has by now been clearly settled for some Chironomus species, at least; specimens that had fed on sucrose flew far longer than starved specimens, and starved females longer than starved males, which suggested they had eclosed with larger reserves of energy than the males. Some authors suggest the females and males apply the resources obtained in feeding differently. Males expend the extra energy on flight, while females use their food resources to achieve longer lifespans. The respective strategies should be compatible with maximal probability of successful mating and reproduction in those species that do not mate immediately after eclosion, and in particular in species that have more than one egg mass maturing, the less developed masses being oviposited after a delay. Such variables also would be relevant to species that exploit wind for dispersal, laying eggs at intervals. Chironomids that feed on nectar or pollen may well be of importance as pollinators, but current evidence on such points is largely anecdotal. However, the content of protein and other nutrients in pollen, in comparison to nectar, might well contribute to the females' reproductive capacities.[2]
Adults can be pests when they emerge in large numbers. They may cause difficulty during driving if they collide with the windshield, creating an opaque coating which obscures the driver's vision.[14] They can damage paint, brick, and other surfaces with their droppings. When large numbers of adults die, they can build up into malodorous piles. They can provoke allergic reactions in sensitive individuals.[15]
Chironomidae had variable feeding ecology, most species feed on algae and other small soil organisms they can filtrate.[16][17] Larvae and pupae are important food items for fish, such as trout, banded killifish, and sticklebacks, and for many other aquatic organisms as well such as newts. Many aquatic insects, such as various predatory hemipterans in the families Nepidae, Notonectidae, and Corixidae eat Chironomidae in their aquatic phases. So do predatory water beetles in families such as the Dytiscidae and Hydrophilidae. The flying midges are eaten by fish and insectivorous birds, such as swallows and martins. They are also thought to be an especially important food source for tufted duck chicks during their first few days of life. They also are preyed on by bats and flying predatory insects, such as Odonata and dance flies.
The Chironomidae are important as indicator organisms, i.e., the presence, absence, or quantities of various species in a body of water can indicate whether pollutants are present. Also, their fossils are widely used by palaeolimnologists as indicators of past environmental changes, including past climatic variability.[18] Contemporary specimens are used by forensic entomologists as medico-legal markers for the postmortem interval assessment.[19]
A number of chironomid species inhabit marine habitats. Midges of the genus Clunio are found in the intertidal zone, where they have adjusted their entire life cycle to the rhythm of the tides. This made the species Clunio marinus an important model species for research in the field of chronobiology.[20]
Many species are terrestrial living in soil being dominant part of soil fauna community in many wet soil habitats but also in agricultural land and early stages of succession.[21] Chironomidae display various strategies to use various temporary habitats.[22]
Anhydrobiosis is the ability of an organism to survive in the dry state. Anhydrobiotic larvae of the African chironomid Polypedilum vanderplanki can withstand prolonged complete desiccation (reviewed by Cornette and Kikawada[23]). These larvae can also withstand other external stresses including ionizing radiation.[24] The effects of anhydrobiosis, gamma ray and heavy-ion irradiation on the nuclear DNA and gene expression of these larvae were studied by Gusev et al.[24] They found that larval DNA becomes severely fragmented both upon anhydrobiosis and irradiation, and that these breaks are later repaired during rehydration or upon recovery from irradiation. An analysis of gene expression and antioxidant activity suggested the importance of removal of reactive oxygen species as well as the removal of DNA damages by repair enzymes. Expression of genes encoding DNA repair enzymes increased upon entering anhydrobiosis or upon exposure to radiation, and these increases indicated that when DNA damages occurred, they were subsequently repaired. In particular, expression of the Rad51 gene was substantially up-regulated following irradiation and during rehydration.[24] The Rad51 protein plays a key role in homologous recombination, a process required for the accurate repair of DNA double-strand breaks.
The family is divided into 11 subfamilies: Aphroteniinae, Buchonomyiinae, Chilenomyinae, Chironominae, Diamesinae, Orthocladiinae, Podonominae, Prodiamesinae, Tanypodinae, Telmatogetoninae, and Usambaromyiinae.[25][26] Most species belong to Chironominae, Orthocladiinae, and Tanypodinae. Diamesinae, Podonominae, Prodiamesinae, and Telmatogetoninae are medium-sized subfamilies with tens to hundreds of species. The remaining four subfamilies have fewer than five species each.
Two lake flies observed in Neenah, Wisconsin, after the yearly hatch in Lake Winnebago The Chironomidae (informally known as chironomids, nonbiting midges, or lake flies) comprise a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae. Many species superficially resemble mosquitoes, but they lack the wing scales and elongated mouthparts of the Culicidae.
The name Chironomidae stems from the Ancient Greek word kheironómos, "a pantomimist".
